A known type of fluid pressure cylinder includes a cylinder, a piston disposed for displacement in an axial direction in the interior of the cylinder, and a piston rod connected to the piston. The fluid pressure cylinder is constituted such that the piston rod, which is connected to the piston, undergoes movement upon displacement of the piston by a fluid pressure. As a method for joining the piston and the piston rod, generally, a method by way of screw-engagement or a method that involves crimping is adopted. With the screw-engagement method, a screw hole (female screw threads) that penetrates through the piston in the axial direction is provided, whereas male screw threads are provided on one end of the piston rod, and the piston rod is attached directly to the piston by screw-engagement, or alternatively, a drill hole is provided in the piston, and the piston and the piston rod are joined by fastening a nut or the like to one end of the piston rod after the one end is inserted into the drill hole of the piston (see, for example, FIG. 10 of Japanese Laid-Open Utility Model Publication No. 58-123957). With the crimping method, a through hole is provided that penetrates in the axial direction of the piston, and after the piston rod has been inserted into the through hole, a portion of the piston is plastically deformed in order to join the piston and the piston rod to one another (see, for example, FIG. 1 of Japanese Laid-Open Utility Model Publication No. 63-004406).
In the case of the aforementioned screw-engagement method, it is difficult for an airtight state to be maintained by the threads, and therefore, a seal member such as a separate O-ring must be provided on the fastening portion, and a process is required to provide a groove for installation of the seal member. Further, in the case of the screw-engagement method, a certain length for the screw is required in order to impart a strength sufficient to withstand the force generated by the fluid pressure, and it is difficult to shorten the length of the apparatus as a whole.
With the crimping method, in order to provide sealing between the piston and the piston rod, a seal member must be disposed on the fitted portion, and a process is required to provide a groove for installation of the seal member. A certain amount of sealing capability may be imparted by plastic deformation of metal, however, in this case, there is a concern that a sufficient sealing capability cannot be obtained.